The invention relates to an orifice apparatus for use in a system which reduces noxious components of exhaust gas from an engine of an automobile, and more particularly, to such orifice apparatus capable of switching between a plurality of throttle levels for the gas flow.
An exhaust gas purifier system of an engine for an automobile, for example, an ignition timing control system of the spark delay type, employs a negative pressure delay valve including an orifice and a check valve to retard the transmission of a negative pressure to a vacuum angle advance diaphragm of a distributor. A speed reduction control system of the throttle positioner type, having the same function as an orifice and a check valve, is utilized to provide a more open position of a throttle valve during a speed reduction phase than an idle position in order to suppress the exhaust of unburned hydrocarbon.
However, the use of an orifice having a fixed throttle in these conventional exhaust gas purifier systems causes an accumulation of operational errors of various devices used in the system, resulting in a difficulty to achieve an optimum matching between exhaust gas, operating characteristic and fuel cost from vehicle to vehicle.